The thermoelectric effect refers to the conversion between temperature differences and electric voltage, which can be observed in thermoelectric materials. Thermoelectric materials are finding use in fields such as electricity generation (e.g., recovery electrical energy from waste heat), cooling (e.g., cooling integrated circuits), and heating (e.g., precision heating applications such as polymerase chain reaction machines).
Controlling the thermal conductivity of a material independently of its electrical conductivity continues to be a goal for researchers working on thermoelectric materials for use in, for example, energy applications and in the cooling of integrated circuits. In principle, the thermal conductivity (κ) and the electrical conductivity (σ) may be independently optimized in semiconducting nanostructures because different length scales are associated with phonons (which carry heat) and electric charges (which carry current). Phonons are scattered at surfaces and interfaces, so κ generally decreases as the surface-to-volume ratio increases (e.g., as the material becomes thinner). In contrast, σ is less sensitive to a decrease in nanostructure size, although, at sufficiently small nanostructure sizes, electrical conductivity will degrade through the scattering of charge carriers at interfaces. As such, it may be difficult to independently control the thermal conductivity κ and the electrical conductivity σ of a thermoelectric material.